One or more embodiments of the present disclosure relate to an active matrix organic light emitting diode (AMOLED) panel, a driving circuit and driving method for the AMOLED panel.
As compared with conventional thin film transistor liquid crystal display (TFT-LCD) panels, AMOLED panels have advantages such as faster response speed, higher contrast, wider view angles, and so on, and thus are regarded as the next generation of display technology, drawing much attention from most of the developers in display technology.
A sub-pixel unit of an AMOLED panel emits light is driven by a driving circuit. A conventional 2T1C driving circuit for each sub-pixel unit comprises two transistors (2T) and one capacitor (1C), as illustrated in FIG. 1. In FIG. 1, a transistor M1 acts as a switching transistor, a transistor M2 acts as a driving transistor, and a capacitor C acts as a storage capacitor. The transistor M1 is controlled by a row scan line signal Vscan so as to control the input of a data voltage Vdata. The transistor M2 is used for controlling an organic light emitting diode (OLED) to emit light. The storage capacitor C is used for providing a maintaining voltage to the gate of the transistor M2.
FIG. 2 is a control timing chart of the conventional 2T1C driving circuit in FIG. 1. The operation procedure of the 2T1C driving circuit is as follows. Two stages T1, T2 in FIG. 2 are taken for example, wherein the stage T1 is a writing stage of the display data voltage and the stage T2 is a display maintaining stage. During the stage T1, the row scan line signal Vscan is at a high level, and the transistor M1 is turned on, thus the data voltage Vdata charges the storage capacitor C and the data voltage Vdata is transferred to the gate of the transistor M2 at the same time, such that the transistor M2 works in a saturation status, and the organic light emitting diode (OLED) is driven to emit light. During the stage T2, the row scan line signal Vscan is changed to a low level, and the transistor M1 is turned off, so the data voltage Vdata cannot reach the gate of the transistor M2 and the storage capacitor C provides the gate of the transistor M2 with the maintaining voltage, such that the transistor M2 continues to work in the saturation status, which makes the OLED emit light continuously. Thereafter, the 2T1C driving circuit repeats the stage T2 until next stage T1 arrives.
It can be known from the above that the OLED in each pixel of the AMOLED panel is capable of emitting light with a driving current generated when the driving transistor M2 works in the saturation status. In particular, the driving current (i.e., the current flowing through the OLED) I=K(Vgs−Vth)2, wherein Vg, is a voltage difference between the gate and source of the transistor M2, Vth is a threshold voltage of the transistor M2, and K is a constant related to the structure and the manufacturing process of the transistor M2 per se. At present, the threshold voltages V1, of transistors have bad uniformity in the low temperature poly-silicon process, and may shift in usage, thus different threshold voltages of the transistor M2 result in different driving currents over time even if a same data voltage Vdata is input to the gate of the transistor M2, which makes worse brightness uniformity for the AMOLED panel.